Field of Invention
The present invention relates to treatment of urban domestic refuse, and more particularly to a method for sorting and comprehensively utilizing municipal solid waste. Especially, different ingredients such as organic matter, magnetic substances, plastics and fabrics of the refuse are efficiently sorted by a mechanical method. Then different reutilization methods are applied according to different substances sorted, for achieving reduction, harmlessness, and reutilization of the refuse.
Description of Related Arts
With the rapid development of Chinese economy, the amount of urban domestic refuse generated rapidly growths. In 2010, Chinese urban domestic refuse disposed is amounted to 150 million tons, and over 80 acres of lands are occupied for landfill and storage of the refuse. ⅔ of large and medium-sized cities in China have been surrounded by refuse, and ¼ of the cities in China have no suitable place for refuse. Furthermore, it is difficult to find site for and construct new refuse dump. For example, in Xi'an, the average daily production of refuse is about 5,600 tons, and there is only one landfill site at Jiangcungou, which brings great risk to refuse treatment. A new landfill site has been planned for several years, but construction is not able to start because of social resistance. It is expected that in 2020, a total amount of urban domestic refuse disposed will up to 250 million tons. Waste disposal problem is imminent.
Conventionally, landfill, compost and incineration methods are mainly utilized for refuse disposal in China, and are not able to thoroughly achieve harmlessness and reutilization of domestic refuse.
First, the landfill method: The refuse disposed by the landfill method is more than 85% of a total amount of refuse in China. CH4-rich landfill gas is easy to be generated in the landfill site. As a result, explosion occurred in Guangdong, Yunnan, etc. Furthermore, the landfill site will generate a lot of refuse leachate, which comprises toxic organic chemical pollutants such as heavy metals, and a lot of pathogens as well as viruses, which may infiltrate to groundwater and cause serious groundwater pollution. The leachate of a refuse dump near the Hexi water source of Yongding River in Beijing was not handled properly, which results in safety risk of drinking water for 10 million people in the area.
Second, the incineration method: The refuse disposed by the incineration method is approximately 9% of the total amount of refuse in China. By incineration, thermal energy inside the refuse is efficiently used and a weight of the refuse is reduced by more than 75%. However, highly toxic carcinogen “dioxins” is easy to be generated during the refuse incineration, and fly ash generated by incineration comprises a large amount of heavy metals, which are hazardous refuse and improper treatment thereof will cause serious pollution. Furthermore, the heavy metals and dioxins are difficult to be online-monitored, and treatment thereof is expensive. As a result, environmental protection investment is more than ⅓ of a total investment of a refuse incineration generation station, and emissions standards are still difficult to achieve. Conventionally, in Guangzhou and other places, a number of refuse incineration generation stations have been forced outage among the public pressure. In developed countries such as United States and Japan, refuse incineration generation stations were continuously shut down since 2000.
Third, the compost method: The refuse disposed by the compost method is about 4% of the total amount of refuse in China. By the compost method, the refuse is reutilized. However, sorting during the compost method is not thorough, and plastic, iron, glass and other materials will be left in fertilizer raw materials. As a result, the fertilizer produced is not clean, products lose value as a fertilizer, soil is polluted, and crops are harmed. A reduction rate of the compost method is up to 70%, and more than 30% of residue thereof needs further disposal.
Conventionally, Chinese government and environmental health departments put more and more emphasis on sorting and comprehensively utilizing technology of refuse. The technology integrates refuse sorting and reutilization methods such as incineration, landfill and compost. Firstly, the refuse materials which are able to be reutilized are sorted corresponding to each reutilization methods, and the sorted materials are able to be utilized according to different reutilization methods.
According to analysis of refuse sorting and utilizing technology in China, conventional problems to be solved are as follows:
Firstly, sorting equipment and technology are not optimized corresponding to refuse characteristics in China. Conventionally, technology and equipment applied in China are mainly conventional sorting techniques in fields such as agriculture and mining, which is not optimized corresponding to complex components and high moisture content of the refuse. As a result, useful substances such as paper and plastic in refuse are not efficiently sorted and recycled.
Secondly, refuse sorting equipments are not mechanized, automatized, or systematized. Several comprehensive refuse treatment stations were closed, which proves that manual sorting or simple integration of a single device is not able to efficiently sort, and different sorting methods should be taken advantage of, for integrating different sorting equipments in one system.
Thirdly, no sorting method is designed for different characteristics of the urban domestic refuse. Composition of the urban domestic refuse is very complex, and domestic refuse of different cities is quite different. For different refuse composition, using the same refuse sorting equipment may cause low sorting efficiency and reduce the quality of investment. Furthermore, the equipments needing investment and construction are not strengthened, and non-essential equipments cause a refuse of money. Therefore, a success refuse sorting experience of one city is not necessarily appropriate for another city. A sorting system should be designed corresponding to domestic refuse characteristics of the city, and parameters of equipments of the system should be optimized. However, most design institutes and sorting equipment manufacturers have insufficient understanding of difficulty of refuse sorting in China, and study little about refuse composition variability and optimization of operating parameters of sorting equipment and systems, which worsen the operation of the domestic refuse sorting system built in China (the vast majority thereof have been completed in the outage state), the actual operation of the equipment are difficult to meet the design requirements.
Fourthly, recycling method of sorted product is not well researched, and the economic value of sorted product has not been fully reflected. The conventional sorting technology in China is not able to effectively combine the recycling technology and the sorting process. Overall economy of sorting, recycling and reusing is not high.